1. Field of the Invention
The present invention relates to a manufacturing method for a device having an electrostatic actuator, such as a inkjet head, and relates particularly to the bonding temperature used in the anodic bonding process of the manufacturing method.
2. Description of the Related Art
Anodic bonding as a method for firmly fixing one piece or substrate to another is known. A typical anodic bonding process comprises a first step of heating the substrates to be bonded up to a certain bonding temperature, a second step of maintaining the substrates at the bonding temperature for a predetermined first period of time, a third step of applying a high voltage between the substrates for a predetermined second period of time, a fourth step of maintaining the substrates at the bonding temperature for a predetermined third period of time with the voltage removed, and a fifth step during which the bonded substrates cool down to room temperature.
Descriptions of inkjet heads are found in, for example, JP-A-80252/1990 and JP-A-289351/1990. The inkjet head discussed in JP-A-80252/1990 is a so-called "ink-on-demand" type head and, in particular, employs an electrostatic attraction force applied to the actuator to achieve high quality (i.e., high resolution) printing. Such inkjet head is constructed using anodic bonding to bond substrates, diaphragms, and other components thereof. In such an arrangement, anodic bonding retains approximately 40% of the strength of the base material, and has thus been used as an effective bonding method for the manufacture of inkjet heads of this type.
Further, electrostatically deformable thin silicon membranes being capable of deformation by electrostatic forces are discussed in U.S. Pat. Nos. 4,203,128 and 4,234,361.
Inkjet heads that are driven by an electrostatic attraction force acting on the actuator are typically manufactured from an ink flow channel substrate (Si) comprising the diaphragms and are disposed between a cover glass (constituted by, for example, borosilicate glass, Pyrex.RTM. glass) and an electrode glass (constituted by, for example, borosilicate glass, Pyrex.RTM. glass). The preferred method of bonding this substrate with the glass during inkjet head manufacture is by anodic bonding. This method is preferred due to the favorable characteristics relating to strength and the required precision of the gap between the diaphragms and electrodes. To improve printer resolution and enable the inkjet head to be driven at the low voltages commonly used in printers, the diaphragms must be formed thinner than the glass arranged on both sides of the diaphragms. Depending on the bonding conditions, however, the diaphragms may be deformed and warp, preventing the inkjet head from functioning normally.
Such problems are not limited exclusively to inkjet heads. The aforementioned problems may also occur in the case of the electrostatic actuator or device, such which may also be produced by means of anodically bonding.
3. Objects of the Invention
Therefore, the object of the present invention is to provide a manufacturing method for devices using the electrostatic actuator which overcomes the aforementioned problems.
It is another object of the present invention to provide an inkjet head comprising diaphragms or thin membranes which are prevented from warping as a result of the anodic bonding process.